Organic light emitting display panel having sub-pixels with different coupling capacitors

ABSTRACT

An organic light emitting display panel includes a first sub-pixel, a second sub-pixel, and a third sub-pixel for respectively emitting differently colored lights, each of the sub-pixels including a switching transistor connected to a data line, and having a gate electrode configured to receive a scan signal, a driving transistor connected to the switching transistor, an emission control transistor connected to the driving transistor, and having a gate electrode configured to receive an emission control signal, an emission control line connected to the gate electrode of the emission control transistor, an organic light emitting diode connected the emission control transistor, and coupling capacitor including a first electrode including a portion of the emission control line, and a second electrode including an anode of the organic light emitting diode overlapping the portion of the emission control line, wherein capacitances of a first capacitor including the coupling capacitor of the first sub-pixel and a second capacitor including the coupling capacitor of the second sub-pixel are greater than a capacitance of a third capacitor including the coupling capacitor of the third sub-pixel.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.16/056,453, filed Aug. 6, 2018, which is a continuation of U.S. patentapplication Ser. No. 15/134,171, filed Apr. 20, 2016, now U.S. Pat. No.10,043,450, which claims priority to and the benefit of Korean PatentApplication No. 10-2015-0154214, filed Nov. 4, 2015, the entire contentof all of which is incorporated herein by reference.

BACKGROUND 1. Field

Example embodiments of the inventive concept relate to display devices,and to organic light emitting display panels having a plurality ofpixels.

2. Description of the Related Art

An organic light emitting display device is able to display an imageusing sub-pixels, for example, a red sub-pixel, a blue sub-pixel, and agreen sub-pixel. The organic light emitting display device may use anAMOLED Impulsive Driving (AID) dimming method, which adjusts on/offduties of an emission control signal when the organic light emittingdisplay device displays a low-luminance/low-grayscale image that is lessthan or equal to about 100 nit to improve luminance uniformity and colorbalance.

However, organic light emitting diodes in the sub-pixels, whichrespectively output different colors of light, have different emissionefficiencies caused by a difference of the characteristics of materials,such that a color difference or luminance difference may be shown at animage of low luminance (or low grayscale), which requires low power. Forexample, when the AID dimming method is performed to display the lowluminance (or low grayscale) image, the luminance of the green sub-pixelincreases, while the luminance of the red and blue sub-pixels decreases,due to a difference of offset direction, so that a screen or the imagehas a defect of a greenish hue.

SUMMARY

Example embodiments provide an organic light emitting display panelincluding sub-pixels, each of which having different capacitance formedin an organic light emitting diode and an emission control line.

According to example embodiments, an organic light emitting displaypanel includes a first sub-pixel, a second sub-pixel, and a thirdsub-pixel for respectively emitting differently colored lights, each ofthe sub-pixels including a switching transistor connected to a dataline, and having a gate electrode configured to receive a scan signal, adriving transistor connected to the switching transistor, an emissioncontrol transistor connected to the driving transistor, and having agate electrode configured to receive an emission control signal, anemission control line connected to the gate electrode of the emissioncontrol transistor, an organic light emitting diode connected theemission control transistor, and coupling capacitor including a firstelectrode including a portion of the emission control line, and a secondelectrode including an anode of the organic light emitting diodeoverlapping the portion of the emission control line, whereincapacitances of a first capacitor including the coupling capacitor ofthe first sub-pixel and a second capacitor including the couplingcapacitor of the second sub-pixel are greater than a capacitance of athird capacitor including the coupling capacitor of the third sub-pixel.

Areas of the first and second electrodes of the first capacitor, andareas of the first and second electrodes of the second capacitor, may berespectively greater than areas of the first and second electrodes ofthe third capacitor.

An area of the anode of the first sub-pixel, and an area of the anode ofthe second sub-pixel, may be respectively greater than an area of thethird sub-pixel.

The first electrode may further include at least a portion of the gateelectrode of the emission control transistor.

The first sub-pixel may be configured to emit red color light, thesecond sub-pixel may be configured to emit blue color light, the thirdsub-pixel may be configured to emit green color light, and an emissionefficiency of the third sub-pixel may be higher than an emissionefficiency of each of the first and second sub-pixels.

The emission control transistor may be configured to receive theemission control signal that swings between an inactive level and anactive level during an emission period within a frame period, theemission period including a period in which the organic light emittingdiode is configured to emit light.

Each of the capacitors may be configured to raise a voltage of thecorresponding anode by coupling based on the emission control signalswing.

Each of the sub-pixels may further include a storage capacitor, thestorage capacitor including a first electrode including a gate electrodeof the driving transistor, and a second electrode including a conductivepattern overlapping the first electrode of the storage capacitor.

Each of the sub-pixels may further include a compensation transistorconnected to the driving transistor for compensating a threshold voltageof the driving transistor, and including a gate electrode configured toreceive the scan signal.

Each of the sub-pixels may further include an initialization transistorconnected to the gate electrode of the driving transistor, and includinga gate electrode configured to receive an initialization signal totransmit an initialization voltage to the gate electrode of the drivingtransistor, and a bypass transistor connected to the anode, andincluding a gate electrode configured to receive a bypass control signalto transmit the initialization voltage to the anode.

The sub-pixels may be arranged in a pentile structure.

Areas of the second electrode of the first capacitor and the secondelectrode of the second capacitor may be respectively greater than anarea of the second electrode of the third capacitor.

The sub-pixels may be arranged in a stripe structure.

Areas of the second electrode of the first capacitor and the secondelectrode of the second capacitor may be respectively greater than anarea of the second electrode of the third capacitor.

According to example embodiments, an organic light emitting displaypanel includes a first sub-pixel, a second sub-pixel, and a thirdsub-pixel for respectively outputting differently colored lights, eachof the sub-pixels including a driving transistor,

a switching transistor, an emission control transistor connected to thedriving transistor, and including a gate electrode configured to receivean emission control signal, an emission control line connected to thegate electrode of the emission control transistor, and an organic lightemitting diode connected to the emission control transistor, andincluding an anode overlapping a portion of the emission control line.

Each of the first and second sub-pixels may further include a couplingcapacitor including a first electrode including the gate electrode ofthe emission control transistor, and a portion of the emission controlline, and a second electrode including a portion of the anode of theorganic light emitting diode overlapping the gate electrode of theemission control transistor and the emission control line.

The gate electrode of the emission control transistor of the thirdsub-pixel and the emission control line might not overlap the anode ofthe organic light emitting diode of the third sub-pixel.

The first sub-pixel may be configured to emit red color light, thesecond sub-pixel may be configured to emit blue color light, the thirdsub-pixel may be configured to emit green color light, and an emissionefficiency of the third sub-pixel may be higher than the emissionefficiency of the first and second sub-pixels.

The gate electrode of the emission control transistor of the thirdsub-pixel and the emission control line of the third sub-pixel mayoverlap the anode of the organic light emitting diode of the thirdsub-pixel.

The third sub-pixel may further include a coupling capacitor including afirst electrode including the gate electrode of the emission controltransistor and a portion of the emission control line, and a secondelectrode including a portion of the anode of the organic light emittingdiode overlapping with the gate electrode of the emission controltransistor and the emission control line, and areas of the first andsecond electrodes of the coupling capacitor of the first sub-pixel, andareas of the first and second electrodes of the coupling capacitor ofthe second sub-pixel, may be respectively greater than areas of thefirst and second electrodes of the coupling capacitor of the thirdsub-pixel.

Therefore, the organic light emitting display panel according to exampleembodiments may include the first through third sub-pixels havingcoupling capacitors that have different capacitances based on theemission efficiency. Each of the coupling capacitors may be formed in acorresponding overlapped area where the emission control line and theanode of each sub-pixel are overlapped. Accordingly, the luminance ofthe sub-pixels having relatively low emission efficiency may beincreased by the operation of the coupling capacitors when the AIDdimming is performed. Thus, the color difference of the sub-pixels inthe low-luminance (the low-grayscale) image may be prevented or reduced.In addition, the greenish defect in the low-luminance/low-grayscaleimage may be prevented or reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

Example embodiments can be understood in more detail from the followingdescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a diagram of a portion of an organic light emitting displaypanel according to example embodiments;

FIG. 2 is a circuit diagram illustrating an example of a sub-pixelincluded in the organic light emitting display panel of FIG. 1;

FIG. 3 is a layout diagram illustrating an example of a plurality oftransistors and a capacitor included in the sub-pixel of FIG. 2;

FIG. 4 is a view taken along the line I-I′ of FIG. 3;

FIG. 5 is a timing diagram illustrating an example of a voltage changeof an anode of an organic light emitting diode included in the sub-pixelof FIG. 2;

FIG. 6 is a timing diagram illustrating another example of a voltagechange of an anode of an organic light emitting diode included in thesub-pixel of FIG. 2;

FIG. 7 is a diagram of a portion of an organic light emitting displaypanel according to example embodiments;

FIG. 8 is a diagram illustrating an example of the organic lightemitting display panel of FIG. 7; and

FIG. 9 is a diagram of an organic light emitting display panel accordingto example embodiments.

DETAILED DESCRIPTION

Features of the inventive concept and methods of accomplishing the samemay be understood more readily by reference to the following detaileddescription of embodiments and the accompanying drawings. Hereinafter,example embodiments will be described in more detail with reference tothe accompanying drawings, in which like reference numbers refer to likeelements throughout. The present invention, however, may be embodied invarious different forms, and should not be construed as being limited toonly the illustrated embodiments herein. Rather, these embodiments areprovided as examples so that this disclosure will be thorough andcomplete, and will fully convey the aspects and features of the presentinvention to those skilled in the art. Accordingly, processes, elements,and techniques that are not necessary to those having ordinary skill inthe art for a complete understanding of the aspects and features of thepresent invention may not be described. Unless otherwise noted, likereference numerals denote like elements throughout the attached drawingsand the written description, and thus, descriptions thereof will not berepeated. In the drawings, the relative sizes of elements, layers, andregions may be exaggerated for clarity.

It will be understood that, although the terms “first,” “second,”“third,” etc., may be used herein to describe various elements,components, regions, layers and/or sections, these elements, components,regions, layers and/or sections should not be limited by these terms.These terms are used to distinguish one element, component, region,layer or section from another element, component, region, layer orsection. Thus, a first element, component, region, layer or sectiondescribed below could be termed a second element, component, region,layer or section, without departing from the spirit and scope of thepresent invention.

Spatially relative terms, such as “beneath,” “below,” “lower,” “under,”“above,” “upper,” and the like, may be used herein for ease ofexplanation to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. It will beunderstood that the spatially relative terms are intended to encompassdifferent orientations of the device in use or in operation, in additionto the orientation depicted in the figures. For example, if the devicein the figures is turned over, elements described as “below” or“beneath” or “under” other elements or features would then be oriented“above” the other elements or features. Thus, the example terms “below”and “under” can encompass both an orientation of above and below. Thedevice may be otherwise oriented (e.g., rotated 90 degrees or at otherorientations) and the spatially relative descriptors used herein shouldbe interpreted accordingly.

It will be understood that when an element, layer, region, or componentis referred to as being “on,” “connected to,” or “coupled to” anotherelement, layer, region, or component, it can be directly on, connectedto, or coupled to the other element, layer, region, or component, or oneor more intervening elements, layers, regions, or components may bepresent. In addition, it will also be understood that when an element orlayer is referred to as being “between” two elements or layers, it canbe the only element or layer between the two elements or layers, or oneor more intervening elements or layers may also be present.

In the following examples, the x-axis, the y-axis and the z-axis are notlimited to three axes of a rectangular coordinate system, and may beinterpreted in a broader sense. For example, the x-axis, the y-axis, andthe z-axis may be perpendicular to one another, or may representdifferent directions that are not perpendicular to one another.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the presentinvention. As used herein, the singular forms “a,” “an,” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises,” “comprising,” “includes,” and “including,” when used inthis specification, specify the presence of the stated features,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof. As used herein, the term “and/or” includes any and allcombinations of one or more of the associated listed items. Expressionssuch as “at least one of,” when preceding a list of elements, modify theentire list of elements and do not modify the individual elements of thelist.

As used herein, the term “substantially,” “about,” and similar terms areused as terms of approximation and not as terms of degree, and areintended to account for the inherent deviations in measured orcalculated values that would be recognized by those of ordinary skill inthe art. Further, the use of “may” when describing embodiments of thepresent invention refers to “one or more embodiments of the presentinvention.” As used herein, the terms “use,” “using,” and “used” may beconsidered synonymous with the terms “utilize,” “utilizing,” and“utilized,” respectively. Also, the term “exemplary” is intended torefer to an example or illustration.

When a certain embodiment may be implemented differently, a specificprocess order may be performed differently from the described order. Forexample, two consecutively described processes may be performedsubstantially at the same time or performed in an order opposite to thedescribed order.

The electronic or electric devices and/or any other relevant devices orcomponents according to embodiments of the present invention describedherein may be implemented utilizing any suitable hardware, firmware(e.g. an application-specific integrated circuit), software, or acombination of software, firmware, and hardware. For example, thevarious components of these devices may be formed on one integratedcircuit (IC) chip or on separate IC chips. Further, the variouscomponents of these devices may be implemented on a flexible printedcircuit film, a tape carrier package (TCP), a printed circuit board(PCB), or formed on one substrate. Further, the various components ofthese devices may be a process or thread, running on one or moreprocessors, in one or more computing devices, executing computer programinstructions and interacting with other system components for performingthe various functionalities described herein. The computer programinstructions are stored in a memory which may be implemented in acomputing device using a standard memory device, such as, for example, arandom access memory (RAM). The computer program instructions may alsobe stored in other non-transitory computer readable media such as, forexample, a CD-ROM, flash drive, or the like. Also, a person of skill inthe art should recognize that the functionality of various computingdevices may be combined or integrated into a single computing device, orthe functionality of a particular computing device may be distributedacross one or more other computing devices without departing from thespirit and scope of the exemplary embodiments of the present invention.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which the present invention belongs. Itwill be further understood that terms, such as those defined in commonlyused dictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and/orthe present specification, and should not be interpreted in an idealizedor overly formal sense, unless expressly so defined herein.

FIG. 1 is a diagram of a portion of an organic light emitting displaypanel according to example embodiments.

Referring to FIG. 1, the organic light emitting display panel 1000 mayinclude a plurality of pixels. Each of the pixels may include a firstsub-pixel PX1, a second sub-pixel PX2, and a third sub-pixel PX3 forrespectively outputting different colors of light.

FIG. 1 shows an arrangement of emission control line EM with respect tothe first through third sub-pixels PX1, PX2, and PX3.

Each of the first through third sub-pixels PX1, PX2, and PX3 may includea plurality of transistors including a driving transistor, an emissioncontrol transistor, etc., and may also include a storage capacitor, acoupling capacitor/coupling capacitance Cma1, Cma2, and Cma3, and anorganic light emitting diode. Here, each of the coupling capacitorsCma1, Cma2, and Cma3 may include a first electrode (e.g., a firstcapacitor plate), which includes a portion of the emission control lineEM, and a second electrode (e.g., a second capacitor plate), whichincludes a respective anode 200A, 200B, and 200C of the organic lightemitting diode that overlaps with the first electrode. The firstelectrode of each of the coupling capacitors Cma1, Cma2, and Cma3 mayfurther include at least a portion of a gate electrode of thecorresponding emission control transistor.

The anodes 200A, 200B, and 200C of the organic light emitting diodes mayrespectively correspond to light emitting regions of the first throughthird sub-pixels PX1, PX2, and PX3. For example, as illustrated in FIG.1, the light emitting regions of the first and second sub-pixels PX1 andPX2 may be greater than the light emitting region of the third sub-pixelPX3 (e.g., the size of the light emitting regions corresponding to anaperture ratio). In one embodiment, an area of the anode 200A of thefirst sub-pixel PX1 and an area of the anode 200B of the secondsub-pixel PX2 may each be greater than an area of the anode 200C of thethird sub-pixel PX3. Accordingly, sizes of the coupling capacitorsbetween the anodes 200A, 200B, and 200C of the organic light emittingdiodes and the emission control line EM may be designed differently.Thus, when an AMOLED impulsive driving (AID) dimming method is performedin a low-luminance area, coupling voltages (or increased voltages) bythe coupling capacitors Cma1, Cma2, and Cma3 according to the sub-pixelsPX1, PX2, and PX3 may be different. Here, the AID dimming methodadjusts/controls on/off duties of an emission control signal to adjustthe luminance. The AID dimming method is performed in the low-luminancearea producing luminance that is below about 110 nit (cd/m²).

Each of the coupling capacitors Cma1, Cma2, and Cma3 may extract partialvoltage of the emission control signal to the anodes 200A, 200B, and200C of the organic light emitting diodes based on a fluctuation of theemission control signal. Thus, voltages of the anodes 200A, 200B, and200C of the organic light emitting diodes may be changed, or mayfluctuate, by the coupling of the coupling capacitors Cma1, Cma2, andCma3, respectively (e.g., by extracting the partial voltage of theemission control signal).

Hereinafter, the first capacitor Cma1 is the coupling capacitor of thefirst sub-pixel PX1, the second capacitor Cma2 is the coupling capacitorof the second sub-pixel PX2, and the third capacitor Cma3 is thecoupling capacitor of the third sub-pixel PX3. Capacitances of the firstand second capacitors Cma1 and Cma2 may be greater than a capacitance ofthe third capacitor Cma3. Here, the capacitances of the first and secondcapacitors Cma1 and Cma2 may be substantially the same, or may bedifferent. In addition, the capacitances of the first through thirdcapacitors Cm1, Cma2, and Cma3 may have values determined based on therespective emission efficiencies of the organic light emitting diodes.In one embodiment, the areas of the first and second electrodes of thefirst capacitor Cma1, and areas of the first and second electrodes ofthe second capacitor Cma2, may be greater than areas of the first andsecond electrodes of the third capacitor Cma3. Accordingly, asillustrated in FIG. 1, the overlapped portions between the emissioncontrol line EM and the anodes 200A, 200B, and 200C of the organic lightemitting diodes may be the first through third capacitors Cm1, Cma2, andCma3, respectively. Also, each of the first through third sub-pixelsPX1, PX2, and PX3 may include two emission control transistors. Gateelectrodes of the emission control transistors may be connected to theemission line EM. Thus, the gate electrodes of the emission controltransistors may be considered to be part of the emission control lineEM.

In one embodiment, the first sub-pixel PX1 may emit red color light, thesecond sub-pixel PX2 may emit blue color light, and the third sub-pixelPX3 may emit green color light. Here, the emission efficiency of thethird sub-pixel PX3 may be relatively higher than the emissionefficiencies of the first and second sub-pixels PX1 and PX2. However,this is only an example, and the colors of light emitted from thesub-pixels PX1, PX2, and PX3 are not limited thereto. For example,colors of light may be determined by the emission efficiencies of thesub-pixels PX1, PX2, and PX3.

When the AID dimming method is performed, the voltages of the anodes200A and 200B of the first and second sub-pixels PX1 and PX2 may beraised by the coupling of the first and second capacitors Cma1 and Cma2,respectively. Thus, the luminance of the first and second sub-pixels PX1and PX2 may be increased. Also, the color difference, or the luminancedifference, between the third sub-pixel PX3 and the first and secondsub-pixels PX1 and PX2, which is due to differences of the emissionefficiency, may be reduced. Therefore, a greenish hue in a displayedimage when the organic light emitting display panel 1000 displays thelow-luminance/low-grayscale image may be prevented or reduced.

FIG. 2 is a circuit diagram illustrating an example of a sub-pixelincluded in the organic light emitting display panel of FIG. 1, FIG. 3is a layout diagram illustrating an example of a plurality oftransistors and a capacitor included in the sub-pixel of FIG. 2, andFIG. 4 is a view taken along the line I-I′ of FIG. 3.

Referring to FIGS. 2, 3, and 4, a sub-pixel in the organic lightemitting display panel 1000 may include a switching transistor T2connected to a data line 171 and having a gate electrode configured toreceive a scan signal GW (or Sn), and may also include a drivingtransistor T1 connected to the switching transistor T2, an emissioncontrol transistor(s) T5 and T6 connected to the driving transistor T1and having a gate electrode(s) configured to receive an emission controlsignal Em, an emission control line 123 connected to the gate electrodeof the emission control transistor(s) T5 and T6, an organic lightemitting diode EL connected the emission control transistor(s) T5 andT6, and a coupling capacitor/coupling capacitance Cma having a firstelectrode, which includes a portion of the emission control line 123,and having a second electrode, which includes an anode of the organiclight emitting diode EL overlapping with the first electrode (i.e.,overlapping with the emission control line 123). Here, the transistor T5may be referred to as an operation control transistor.

In one embodiment, the sub-pixel may further include a storage capacitorCst, a compensation transistor T3, an initialization transistor T4, anda bypass transistor T7.

The sub-pixel may also include a scan line 121, an initialization line122, the emission control line 123, and a bypass control line 128, whichrespectively apply a scan signal GW (e.g., Sn), an initialization signalGI (e.g., Sn−1), the emission control signal Em, and a bypass controlsignal GB (e.g., Sn+1). These lines 121, 122, 123, and 128 may extend ina row direction. The sub-pixel may also include the data line 171 and adriving voltage line 175, which cross the scan line 121, theinitialization line 122, the emission control line 123, and the bypasscontrol line 128. The data line 171 and the driving voltage line 175 mayapply a data signal DATA and a driving voltage ELVDD, respectively. Aninitialization voltage VINT may be transferred to the driving transistorT1, via initialization transistor T4, through an initialization voltageline 124.

The driving transistor T1 may include a gate electrode connected to afirst electrode of the storage capacitor Cst, a source electrodeconnected to the driving voltage line 175 via the operation controltransistor T5, and a drain electrode electrically connected to the anodeof the organic light emitting diode EL via the emission controltransistor T6. The driving transistor T1 may receive the data signalDATA according to a switching operation of the switching transistor T2,and may supply a driving current to the organic light emitting diode EL.

The switching transistor T2 may include a gate electrode connected tothe scan line 121, a source electrode connected to the data line 171,and a drain electrode connected to the source electrode of the drivingtransistor T1. The switching transistor T2 may be turned on according tothe scan signal GW received through the scan line 121, and may transmitthe data signal DATA from the data line 171 to the source electrode ofthe driving transistor T1.

The compensation transistor T3 may include a gate electrode connected tothe scan line 121, a source electrode connected to the drain electrodeof the driving transistor T1, and a drain electrode connected to thefirst electrode of the storage capacitor Cst, which is also connected toa drain electrode of the initialization transistor T4 and the gateelectrode of the driving transistor T1. The compensation transistor T3may be turned on according to the scan signal GW to diode-connect thedriving transistor T1, such that a threshold voltage of the drivingtransistor T1 may be compensated.

The initialization transistor T4 may include a gate electrode connectedto the initialization line 122, a source electrode connected to theinitialization voltage line 124, and a drain electrode connected to thedrain electrode of the compensation transistor T3 and connected to thegate electrode of the driving transistor T1. The initializationtransistor T4 may be turned on according to the initialization signal GIto transmit the initialization voltage VINT to the gate electrode of thedriving transistor T1, such that the gate voltage of the drivingtransistor T1 may be initialized.

The operation control transistor T5 may include a gate electrodeconnected to the emission control line 123, a source electrode connectedto the driving voltage line 175, and a drain electrode connected to thesource electrode of the driving transistor T1.

The emission control transistor T6 may include a gate electrodeconnected to the emission control line 175, a source electrode connectedto the drain electrode of the driving transistor T1 and connected to thesource electrode of the compensation transistor T3, and a drainelectrode connected to the anode of the organic light emitting diode EL.The operation control transistor T5 and the emission control transistorT6 may be concurrently turned on according to the emission controlsignal Em, such that the driving current may flow into the organic lightemitting diode EL.

The bypass transistor T7 may include a gate electrode connected thebypass control line 128, a source electrode connected to the drainelectrode of the emission control transistor T6 and connected to theanode of the organic light emitting diode EL, and a drain electrodeconnected to the initialization voltage line 124.

The first electrode of the coupling capacitor Cma may include the gateelectrode of the emission control transistor T6, the gate electrode ofthe operation control transistor T5, and a portion of the emissioncontrol line 123. The second electrode of the coupling capacitor Cma mayinclude the anode 200 of the organic light emitting diode EL overlappingwith the first electrode of the coupling capacitor Cma (i.e.,overlapping with the emission control line 123). When AID dimming isperformed, a voltage of the anode 200 of the organic light emittingdiode EL (i.e., an anode voltage) may be changed/raised by the coupling,or by extracting the partial voltage of the emission control signal Emof the coupling capacitor Cma.

The coupling capacitor Cma may be formed according to the color of lightemitted from the respective sub-pixel. In one embodiment, thecapacitances of the first and second capacitors Cma1 and Cma2 may begreater than the capacitance of the third capacitor Cma3 when theemission efficiency of the third sub-pixel PX3 is higher than theemission efficiencies of the first and second sub-pixels PX1 and PX2.For example, the areas of the first and second electrodes of the firstcapacitor Cma1, and the areas of the first and second electrodes of thesecond capacitor Cma2, may be greater than the areas of the first andsecond electrodes of the third capacitor Cma3. Thus, amounts of raisedanode voltages of the first and second sub-pixels PX1 and PX2 may begreater than amount of raised anode voltage of the third sub-pixel PX3when the AID dimming is performed. Thus, the color difference of thesub-pixels caused by the difference of the emission efficiency may beprevented or reduced.

A first electrode of the storage capacitor Cst may include the gateelectrode of the driving transistor T1, and a second electrode of thestorage capacitor Cst may include a conductive pattern overlapping thefirst electrode of the storage capacitor Cst (i.e., overlapping with thegate electrode of the driving transistor T1). The conductive pattern maybe a portion of the driving voltage line 175 that overlaps the gateelectrode of the driving transistor T1. A cathode of the organic lightemitting diode EL may be connected to a common voltage ELVSS.Accordingly, the organic light emitting diode EL may receive the drivingcurrent from the driving transistor T1 to emit light of a certain color.

The driving transistor T1, the switching transistor T2, the compensationtransistor T3, the initialization transistor T4, the operation controltransistor T5, the emission control transistor T6, and the bypasstransistor T7 may be formed along a semiconductor layer 131. Thesemiconductor layer 131 may be curved in various shapes.

The semiconductor layer 131 may be made of, for example, polysilicon oroxide semiconductor. The oxide semiconductor may include one of an oxidebased on titanium (Ti), hafnium (Hf), zirconium (Zr), aluminum (Al),tantalum (Ta), germanium (Ge), zinc (Zn), gallium (Ga), tin (Sn), indium(In), zinc oxide (ZnO), indium-gallium-zinc oxide (InGaZnO4), indiumzinc oxide (Zn—In—O), zinc-tin oxide (Zn—Sn—O), indium gallium oxide(In—Ga—O), indium-tin oxide (In—Sn—O), indium-zirconium oxide (In—Zr—O),indium-zirconium-zinc oxide (In—Zr—Zn—O), indium-zirconium-tin oxide(In—Zr—Sn—O), indium-zirconium-gallium oxide (In—Zr—Ga—O),indium-aluminum oxide (In—Al—O), indium-zinc-aluminum oxide(In—Zn—Al—O), indium-tin-aluminum oxide (In—Sn—Al—O),indium-aluminum-gallium oxide (In—Al—Ga—O), indium-tantalum oxide(In—Ta—O), indium-tantalum-zinc oxide (In—Ta—Zn—O), indium-tantalum-tinoxide (In—Ta—Sn—O), indium-tantalum-gallium oxide (In—Ta—Ga—O),indium-germanium oxide (In—Ge—O), indium-germanium-zinc oxide(In—Ge—Zn—O), indium-germanium-tin oxide (In—Ge—Sn—O), indium-germaniumgallium oxide (In—Ge—Ga—O), titanium-indium-zinc oxide (Ti—In—Zn—O),and/or hafnium-indium-zinc oxide (Hf—In—Zn—O), which are complex oxides.When the semiconductor layer 131 is made of an oxide semiconductor, aseparate passivation layer may be added to protect the oxidesemiconductor from damage resulting from high temperatures and/or otherexternal influences.

The semiconductor layer 131 may include a channel region, a sourceregion, and a drain region. The channel region may allow for formationof a channel, and may be doped with N-type impurity or P-type impurity.The source and drain regions may be formed at respective sides of thechannel region, and may be formed by doping a doped impurity having aconductivity type opposite to the conductivity type of the channelregion.

Hereinafter, an example of a construction of the sub-pixel including thedriving transistor T1, the switching transistor T2, and the emissioncontrol transistor T6 will be described referred to FIG. 4.

A buffer layer 120 may be disposed on a substrate 110. The substrate mayinclude insulation materials, such as a glass, quartz, ceramic, plastic,or etc.

A driving semiconductor layer 131, a switching semiconductor layer 132,and an emission control semiconductor layer 133 may be disposed on thebuffer layer 120. The driving semiconductor layer 131 may include adriving source region 131 b and a driving drain region 131 c, which faceeach other with a driving channel region 131 a therebetween. Theswitching semiconductor layer 132 may include a switching source region132 b and a switching drain region 132 c, which face each other with aswitching channel region 132 a therebetween. The emission controlsemiconductor layer 133 may include a emission control source region 133b and a emission control drain region 133 c, which face each other witha emission control channel region 133 a therebetween.

A first gate insulation layer 142 may be on the driving semiconductorlayer 131, on the switching semiconductor layer 132, and on the emissioncontrol semiconductor layer 133.

A driving gate electrode 151 may be on the first gate insulation layer142 overlapping the driving channel region 131 a. A switching gateelectrode 152 may be disposed on the first gate insulation layer 142overlapping the switching channel region 132 a. An emission control gateelectrode 153 may be on the first gate insulation layer 142 overlappingthe emission control channel region 133 a. The scan line 121 may beconnected to the switching gate electrode 152, and may be located on thesame layer as the switching gate electrode 152. The emission controlline 123 may be connected to the emission control gate electrode 153,and may be located on the same layer as the emission control gateelectrode 153. The driving gate electrode 151 may include the firstelectrode of the storage capacitor Cst.

A second gate insulation layer 144 may be disposed on the driving gateelectrode 152, the switching gate electrode 151, the emission controlgate electrode 153, the scan line 121, and the emission control line123. The first and second gate insulation layers 142 and 144 may beformed of silicon nitride (SiNx) or silicon oxide (SiO2).

The conductive pattern 126, at least a portion of which acting as thesecond electrode of the storage capacitor Cst, may be on the second gateinsulation layer 144.

An insulation interlayer 160 may be located on the second gateinsulation layer 144 and the conductive pattern 126. The insulationinterlayer 160 may include ceramic-based materials, such as siliconnitride (SiNx), silicon oxide (SiO2), etc.

The data line 171 including a switching source electrode 172 (i.e., thesource electrode of the switching transistor T2), the driving voltageline 175 for transmitting the driving voltage ELVDD, a connecting member174 to connect the driving gate electrode 151 and the drain electrode ofthe compensation transistor T3, and an emission control drain electrode173 (i.e., the drain electrode of the emission control transistor T6)may all be located on the insulation interlayer 160.

The switching source electrode 172 may be connected to the switchingsemiconductor layer 132 via a contact hole 62. The emission controldrain electrode 173 may be connected to the emission controlsemiconductor layer 133 via a contact hole 63. The driving voltage line175 may be connected to the second electrode 126 of the storagecapacitor Cst via a contact hole 67. An end of the connecting member 174may be connected to the driving gate electrode 151 via the contact hole61.

A passivation layer 180 may be on the insulation interlayer 160 to coverthe data line 171, the driving voltage line 175, etc.

A pixel electrode (i.e., the anode) 200 may be on the passivation layer180. The pixel electrode 200 may be connected to the emission controlgate electrode 173 via a contact hole 81.

A partition wall 350 may be on the passivation layer 180 and on an edgeof the pixel electrode 200. The partition wall 350 may have an openingexposing the pixel electrode 200. The partition wall 350 may be made of,for example, a resin, such as polyacrylates resin, polyimides, and/or asilica-based inorganic material.

An organic light emission layer 370 may be disposed on the exposed pixelelectrode 200. A common electrode (i.e., the cathode) 270 may be on theorganic light emission layer 370. As such, the organic light emittingdiode 70, which includes the pixel electrode 200, the organic emissionlayer 370, and the common electrode 270, may be formed.

Here, the portion of the pixel electrode/anode 200 may overlap theemission control gate electrode 153 (i.e., the gate electrode of theemission control transistor T6) and may overlap a portion of theemission control line 123. Thus, the overlapped portions may causecoupling capacitance, and may be referred to as, or may act as, thecoupling capacitor Cma.

The sub-pixel may include the first sub-pixel PX1 for emitting the redcolor light, the second sub-pixel PX2 for emitting the blue color light,and the third sub-pixel PX3 for emitting the green color light. Here,the capacitance of the coupling capacitor Cma of the sub-pixel havingrelatively high emission efficiency may be set lower than the couplingcapacitor Cma of the sub-pixel having relatively low emissionefficiency. Thus, the color difference of the sub-pixels caused bydifference in emission efficiency may be prevented or reduced when theAID dimming is performed.

FIG. 5 is a timing diagram illustrating an example of a voltage changeof an anode of an organic light emitting diode included in the sub-pixelof FIG. 2, and FIG. 6 is a timing diagram illustrating another exampleof a voltage change of an anode of an organic light emitting diodeincluded in the sub-pixel of FIG. 2.

Referring to FIGS. 5 and 6, the anode voltage VA of the organic lightemitting diode EL may be raised/increased by the coupling capacitor Cma.

As illustrated in FIGS. 5 and 6, when the AID dimming is performed, anemission control signal Em may swing a plurality of times between aninactive level H and an active level L during an emission period withina frame period. The emission period may be a period in which the organiclight emitting diode EL emits light. For example, the emission controlsignal Em may periodically swing 4 times or 8 times. As a dimming levelincreases, a length of a period that the emission control signal Em hasthe inactive level H may increase, such that the luminance may therebydecrease. In contrast, as the dimming level decreases, a length of aperiod that the emission control signal Em has the active level L mayincrease, such that the luminance may thereby increase.

FIGS. 5 and 6 illustrate an embodiment of using p-channel metal-oxidesemiconductor (PMOS) transistor. For example, the emission controlsignal Em applied to the gate electrodes of the PMOS transistor may beactivated with a logical low level L. However, this is an example, andthe emission transistor can be replaced with n-channel metal-oxidesemiconductor (NMOS) transistors, and, in such an embodiment, thesignals applied to the gate electrodes of the NMOS transistor can beactivated with a logic high level.

When the emission control signal Em has the active level L, the emissioncontrol transistor T6 may be turned on, and a driving current/emissioncurrent may flow into the organic light emitting diode EL. Here, thedriving current and corresponding luminance may be changed according tothe anode voltage VA. When the emission control signal Em has the activelevel L, the emission control transistor T6 may be turned on, and theanode voltage VA may increase.

When the emission control signal Em changes to the inactive level H(i.e., a rising edge of the emission control signal Em), the emissioncontrol transistor T6 may be turned off. At the same time, the anodevoltage VA may be raised by the coupling capacitor Cma. For example, thecoupling capacitor Cma may extract partial voltage of the emissioncontrol signal Em to the anode. The increment of anode voltage VA may bedetermined by the capacitance of the coupling capacitor Cma. Forexample, as the capacitance of the coupling capacitor increases, theincrement of the anode voltage VA may increase.

Because the emission efficiency of the green sub-pixel is relativelyhigher than the emission efficiencies of the red and blue sub-pixels, ascreen (e.g., the organic light emitting display panel) has a defect ofan unwanted greenish hue when the panel displays alow-luminance/low-grayscale image having a low driving current.Accordingly, as illustrated in FIG. 6, the organic light emittingdisplay panel may raise a red anode voltage VAr (i.e., the anode voltageof the red sub-pixel), and may raise a blue anode voltage VAb (the anodevoltage of the blue sub-pixel), to thereby increase the luminance of thered and blue sub-pixels. In addition, the green anode voltage VAg (i.e.,the anode voltage of the green sub-pixel), may maintain the voltagelevel, or may decrease. Thus, the capacitances of the couplingcapacitors in the red and blue sub-pixels may be greater than thecapacitance of the coupling capacitor in the green sub-pixel. Forexample, the overlapping areas between the anodes of the red and bluesub-pixels and the emission control line may be greater than theoverlapping area between the anode of the green sub-pixel and theemission control line.

Thus, the color difference of the sub-pixels caused by differentemission efficiencies may be prevented or reduced.

FIG. 7 is a diagram of an organic light emitting display panel accordingto example embodiments, and FIG. 8 is a diagram illustrating an exampleof the organic light emitting display panel of FIG. 7.

The organic light emitting display panel of the present exampleembodiments is substantially the same as the organic light emittingdisplay panel explained with reference to FIGS. 1, 2, 3, and 4, with theexception of a construction of the third sub-pixel not including thecoupling capacitor. Thus, the same reference numerals will be used torefer to the same or like parts as those described in the exampleembodiments of FIG. 1, and any repetitive explanation concerning theabove elements will be omitted.

Referring to FIGS. 7 and 8, the organic light emitting display panel1000A and 1000B may include a plurality of pixels. Each of the pixelsmay include a first sub-pixel R, a second sub-pixel B, and a thirdsub-pixel G for respectively outputting different color lights. In oneembodiment, the first through third sub-pixels R, B, and G may bearranged in a pentile structure.

In one embodiment, the first sub-pixel R may emit red color light, thesecond sub-pixel B may emit blue color light, and the third sub-pixel Gmay emit green color light. Each of the first through third sub-pixelsR, B, and G may include a driving transistor, a switching transistor, anemission control transistor connected to the driving transistor andhaving a gate electrode configured to receive an emission controlsignal, an emission control line EM connected to the gate electrode ofthe emission control transistor, and an organic light emitting diodeconnected the emission control transistor. Here, some portions of theemission control line EM may overlap an anode RA of the organic lightemitting diode of the first sub-pixel R and an anode BA of the organiclight emitting diode of the second sub-pixel B. In other words, each ofthe first and second sub-pixels R and B may further include a couplingcapacitor Cma having a first electrode, which includes a portion of theemission control line EM, and a second electrode, which includes theanode RA and BA of the organic light emitting diode overlapping with theportion of the emission control line EM. For example, the first andsecond sub-pixels R and B may be substantially the same as the first andsecond sub-pixels of FIGS. 1, 2, 3, and 4.

In one embodiment, a gate electrode of the emission control transistorof the third sub-pixel G and the emission control line EM might notoverlap the anode GA of the organic light emitting diode of the thirdsub-pixel G. Thus, the third sub-pixel G might not include a couplingcapacitance or the coupling capacitor Cma. The third sub-pixel G mayhave substantially the same constructions as the first and secondsub-pixels R and B, except for the coupling capacitor Cma.

Accordingly, the luminance of the first and second sub-pixels R and Bhaving relatively low emission efficiency may be increased by theoperation of the coupling capacitor Cma when the AID dimming isperformed. Thus, the color difference of the sub-pixels R, G, and B in alow-luminance/low-grayscale image may be prevented or reduced.

As illustrated in FIG. 8, the first through third sub-pixels R, B, and Gmay be arranged in a stripe structure in the organic light emittingdisplay panel 1000B.

In one embodiment, as illustrated in FIG. 1, a portion of the emissioncontrol line EM may overlap the anode GA of the organic light emittingdiode in the third sub-pixel G. Accordingly, the third sub-pixel G mayinclude the coupling capacitor Cma. Here, the areas of the first andsecond electrodes of the coupling capacitor Cma in the first sub-pixelR, and the areas of the first and second electrodes of the couplingcapacitor Cma in the second sub-pixel B, may be greater than areas ofthe first and second electrodes of the coupling capacitor in the thirdsub-pixel G.

FIG. 9 is a diagram of an organic light emitting display panel accordingto example embodiments.

The organic light emitting display panel of the present embodiment issubstantially the same as the organic light emitting display panelexplained with reference to FIGS. 1, 2, 3, and 4, except forarrangements of the emission control line EM and the sub-pixels. Thus,the same reference numerals will be used to refer to the same or likeparts as those described in the example embodiments of FIG. 1, and anyrepetitive explanation concerning the above elements will be omitted.

Referring to FIG. 9, the organic light emitting display panel 1000C mayinclude a plurality of pixels. Each of the pixels may include a firstsub-pixel R, a second sub-pixel B, and a third sub-pixel G forrespectively outputting lights of different colors. In one embodiment,the first through third sub-pixels R, B, and G may be arranged in astripe structure.

In one embodiment, the first sub-pixel R may emit red color light, thesecond sub-pixel B may emit blue color light, and the third sub-pixel Gmay emit green color light.

Some portions of the emission control line EM may overlap an anode RA ofthe organic light emitting diode of the first sub-pixel R, and mayoverlap an anode BA of the organic light emitting diode of the secondsub-pixel B. Each of the first and second sub-pixels R and B may furtherinclude a coupling capacitor Cma due to the overlap between the anodesRA and BA and the emission control line EM.

The emission control line EM may be formed to reduce or minimize anoverlapped area with the anode GA of the organic light emitting diode ofthe third sub-pixel G. For example, as illustrated in FIG. 9, theemission control line EM may have a curved shape at both ends of theanode GA of the third sub-pixel G, such that the overlapped area betweenthe emission control line EM and the anode GA of the third sub-pixel Gmay be relatively reduced. Thus, the third sub-pixel G may include athird capacitor Cma3 that is smaller than, or has a smaller capacitancethan, first and second capacitors Cma1 and Cma2. In other words, thecapacitance of the third capacitor Cma3 may be less than the first andsecond capacitors Cma1 and Cma2.

In one embodiment, the emission control line EM may have curved shape atboth ends of the anode GA of the third sub-pixel G such that theemission control line EM does not overlap the anode GA of the thirdsub-pixel G. In this case, the third sub-pixel G might not include thethird coupling capacitor Cma3.

As described above, the luminance of the first and second sub-pixels Rand B having relatively low emission efficiency may be increased by theoperation of the coupling capacitor Cma1 and Cma2 when the AID dimmingis performed. Thus, the color difference of the sub-pixels R, G, and Bin a low-luminance/low-grayscale image may be prevented or reduced.

The present embodiments may be applied to any organic light emittingdisplay device and any system including the organic light emittingdisplay device. For example, the present embodiments may be applied to atelevision, a computer monitor, a laptop, a digital camera, a TV, adigital TV, a 3D TV, a cellular phone, a smart phone, a smart pad, apersonal digital assistant (PDA), a portable multimedia player (PMP), aMP3 player, a navigation system, a game console, a video phone, etc.

The foregoing is illustrative of example embodiments, and is not to beconstrued as limiting thereof. Although a few example embodiments havebeen described, those skilled in the art will readily appreciate thatmany modifications are possible in the example embodiments withoutmaterially departing from the novel teachings and advantages of exampleembodiments. Accordingly, all such modifications are intended to beincluded within the scope of example embodiments as defined in theclaims. In the claims, means-plus-function clauses are intended to coverthe structures described herein as performing the recited function andnot only structural equivalents but also equivalent structures.Therefore, it is to be understood that the foregoing is illustrative ofexample embodiments and is not to be construed as limited to thespecific embodiments disclosed, and that modifications to the disclosedexample embodiments, as well as other example embodiments, are intendedto be included within the scope of the appended claims. The inventiveconcept is defined by the following claims, with equivalents of theclaims to be included therein.

What is claimed is:
 1. An organic light emitting display panelcomprising a first sub-pixel, a second sub-pixel, and a third sub-pixel,each of the first and second sub-pixels comprising: a switchingtransistor connected to a data line, and having a gate electrodeconfigured to receive a scan signal; a driving transistor connected tothe switching transistor; an emission control transistor connected tothe driving transistor, and having a gate electrode configured toreceive an emission control signal; an emission control line of which apart is the gate electrode of the emission control transistor; anorganic light emitting diode electrically connected to the drivingtransistor through a via hole; and a coupling capacitor comprising: afirst electrode comprising a portion of the emission control line; and asecond electrode comprising a first electrode layer of the organic lightemitting diode overlapping the portion of the emission control line,wherein capacitances of the coupling capacitors of the first and secondsub-pixels are different.
 2. The panel of claim 1, wherein an entirewidth of the emission control line overlaps the second electrode of afirst capacitor comprising the coupling capacitor of the first sub-pixeland the second electrode of a second capacitor comprising the couplingcapacitor of the second sub-pixel.
 3. The panel of claim 1, wherein thefirst electrode further comprises at least a portion of the gateelectrode of the emission control transistor.
 4. The panel of claim 1,wherein the first sub-pixel is configured to emit red color light,wherein the second sub-pixel is configured to emit blue color light,wherein the third sub-pixel is configured to emit green color light, andwherein an emission efficiency of the third sub-pixel is higher than anemission efficiency of each of the first and second sub-pixels.
 5. Thepanel of claim 1, wherein the emission control transistor is configuredto receive the emission control signal that swings between an inactivelevel and an active level during an emission period within a frameperiod, the emission period comprising a period in which the organiclight emitting diode is configured to emit light.
 6. The panel of claim5, wherein the coupling capacitor is configured to raise a voltage of ananode of the organic light emitting diode by coupling based on theemission control signal swing.
 7. The panel of claim 1, wherein each ofthe first and second sub-pixels further comprises a storage capacitor,the storage capacitor comprising: a first electrode comprising a gateelectrode of the driving transistor; and a second electrode comprising aconductive pattern overlapping the first electrode of the storagecapacitor.
 8. The panel of claim 7, wherein each of the first and secondsub-pixels further comprises: a compensation transistor connected to thedriving transistor for compensating a threshold voltage of the drivingtransistor, and comprising a gate electrode configured to receive thescan signal.
 9. The panel of claim 8, wherein each of the first andsecond sub-pixels further comprises: an initialization transistorconnected to the gate electrode of the driving transistor, andcomprising a gate electrode configured to receive an initializationsignal to transmit an initialization voltage to the gate electrode ofthe driving transistor; and a bypass transistor connected to an anode ofthe organic light emitting diode, and comprising a gate electrodeconfigured to receive a bypass control signal to transmit theinitialization voltage to the anode.
 10. The panel of claim 1, whereinthe first through third sub-pixels are arranged in a pentile structure.11. The panel of claim 1, wherein the first through third sub-pixels arearranged in a stripe structure.